[Intel-gfx] [PATCH] drm/i915: Reject set-tiling-ioctl with stride==0 and a tiling mode

[Chris Wilson]

On Fri, Feb 03, 2017 at 11:34:00AM +0000, Tvrtko Ursulin wrote:
> 
> On 03/02/2017 10:56, Chris Wilson wrote:
> >In commit 957870f93412 ("drm/i915: Split out i915_gem_object_set_tiling()"),
> >I swapped an alignment check for IS_ALIGNED and in the process removed
> >the less-than check. That check turns out to be important as it was the
> >only rejection for stride == 0. Tvrtko did spot it, but I was
> >overconfident in the IS_ALIGNED() conversion.
> >
> >Fixes: 957870f93412 ("drm/i915: Split out i915_gem_object_set_tiling()")
> >Testcase: igt/gem_tiling_max_stride
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >---
> > drivers/gpu/drm/i915/i915_gem_tiling.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
> >index c96140cf47e7..a80f362d2ac1 100644
> >--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
> >+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
> >@@ -173,7 +173,7 @@ i915_tiling_ok(struct drm_i915_gem_object *obj,
> > 	else
> > 		tile_width = 512;
> >
> >-	if (!IS_ALIGNED(stride, tile_width))
> >+	if (!stride || !IS_ALIGNED(stride, tile_width))
> > 		return false;
> >
> > 	/* 965+ just needs multiples of tile width */
> >
> 
> Not sure that I spotted this in the original review, maybe. I got
> thrown off just now by the strange ending of this function in
> thinking is_power_of_2(stride) is last. Perhaps the special case of
> gen < 4 should be an exception and return true the last statement.
> 
> 	if (INTEL_GEN(i915) < 4)
> 		return is_power_of_2(stride);
> 
> 	return true;

That would tidy up the tail, but if we move the pot(stride) check into
the earlier gen4 branch, it would be simpler again.

> Anyway,
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

One patch at a time, thanks.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre